No work to do in new job and constantly bl9cked when I have asked for more work or used my initiativ

I took a promotion about 6 months ago. My line manager is my boss but I actually have a clinical boss too but my line manager is who says what I can and cannot do. My clin8cal boss though she appears not to agree with my line manager does not challenge her. I have now been 6 months in the job. I have no work to do. Every time I engage in work that's agreed, my line manager changes the job and wants it done another way as she feels it is treading on someone else's toes. It's so bad now that I am not now able to fulfill my original job description. Anytime I ask for more work, it's blocked and I don't receive a call or email back about it for over a week. When I try to use my initiate and try to f8nd tasks, I am told not to do so. I am highly trained and the job now does not go anywhere near meeting my l3vel of skill though it is a promotion. My clinical boss appears powerless to intervene. I am feeling demoralised and am losing confidence. I am currently looking for other jobs. Should I approach my line manager again saying that my job does not now concur with my job description, mention that I feel I cannot now even use the most basic level of clinical knowledge or skill in my job. My clinical boss wants me to stay, should I let my line manager know that I am reconsidering whether the job is a goof fit for me given what's occurring. I do somme freelance work,. Money will be tight if I am forced to quit without another post, but I will still be able to eat. It would be helpful if people can let me know what they think might be occurring in this job. I am quite confused by it all.